In the well-known electrostatographic reproduction process, a uniform electric charge is provided to an electrostatographic plate. The plate typically comprises a photoconductive insulating material mounted on a conductive backing. A light image of the subject matter to be reproduced is projected onto the charged plate. Discharging occurs where the light image strikes the plate, thereby resulting information of an electrostatic latent image on the plate. The latent image is developed by applying a developer material, such as a toner, which electrostatically clings to the plate in a visual pattern corresponding to the latent image. Thereafter, the developed image is transferred from the plate to a support material, such as paper or a transparency, to which it may be fixed thereby forming a permanent print on the support material.
The charging step, in which a uniform electric charge is provided to the electrostatic plate, is typically achieved by a corona generating device, which is often referred to in the art as a coronode or a corotron. The corona generating device usually comprises a fine wire, hereinafter a corona wire, made of a good conductor, such as tungsten or platinum. Both ends of the wire are provided with a terminal, to facilitate attachment of the wire to end-blocks, which form part of a corotron wire assembly. One of these endblocks is insulated, whilst the other end-block contains a connector, through which high voltage is applied to the corotron wire.
In an electrostatographic printing apparatus the end-blocks are mounted such that, in use, the corona wire is supported in a tensioned manner. The corona wire is positioned in the apparatus such that its extent is spaced evenly from, and within a chargeable distance of, the electrostatographic plate. Often, the corona wire is partially enclosed by a conductive shield which functions such as to enhance the capacity of the corona wire to provide charge to the plate.
The attachment of the ends of the corona wire to the end-blocks has typically been through releasable, mechanical means of attachment which allow for in-field replacement of the corona wire. A potential issue with such methods of attachment is that, because of the need to carefully adjust the length and tensioning of the wire, relatively complex configurations of the end-blocks are required. Such configurations for example, involve screws and springs, which adds to manufacturing complexity and cost. It also adds to the complexity of any infield service replacement of an old corona wire.
The Applicant has now found that these problems can be ameliorated by the use of a corona wire fixably attached, at each end of the wire, to a terminal made of conducting material. The terminal is shaped such as to be releasably attachable to the end-blocks in a straightforward manner, thereby enabling ease of manufacture and service replacement. Simple terminal shapes are preferred from a cost standpoint. A laser `soldering` method is employed to attach the terminals to the corona wire. Such use of a laser allows for rapid attachment of wire to terminal, and is relatively inexpensive to implement in a manufacturing process on a commercial scale.
In an improvement to the laser `soldering` approach, the Applicant has also defined a manufacturing process having the steps of positioning of a terminal and a corona wire such that a portion of the corona wire touches the terminal at a contact position; directing a laser beam to the contact position thereby causing a soldering action; and subsequently moving the laser relative to the soldered portion to enable trimming off of the end-tip of the wire.
The Applicant has additionally found that if the wire to terminal soldering step is carried out with the wire held at the same tension as it will be held under `in use` (i.e. when included as part of the full corotron wire assembly), and that the terminals at either end of the wire are positioned at the same distance along the wire that they will occupy `in use`, that a corona wire/terminal component may be made to such an accurate length dimension, that said wire terminal component can be attached to the corotron wire assembly without requiring any complex tensioning and/or length adjustment means to be present as part of the assembly. Thus the complex and relatively expensive spring or screw tensioning arrangements of prior art assemblies may be dispensed with.
U.S. Pat. No. 3,790,999 electrophotographic apparatus having a corona wire assembly in which the corona wire is secured in a plastic end-block.
U.S. Pat. No. 4,099,219 a corona wire assembly having beads at each end of the wire and end-block assemblies shaped to receive and releasably retain said beads thereby allowing for tensioning of the wire.
U.S. Pat. No. 4,110,811 describes a corona wire assembly in which the corona wire is supported between insulating end-block assemblies. Each assembly is constructed of mating half-sections which jointly define a substantially closed and insulated cavity lined with a conductive insert.
U.S. Pat. No. 4,112,298 describes a corona wire assembly in which the corona wire is supported between insulating end-blocks. Each end-block has a recess which houses a coil spring through which the wire passes coaxially. The wire is attached to a mass which bears against the loaded coil spring to maintain the wire in a tense condition.
U.S. Pat. No. 5,449,906 describes a corona generating assembly having a plurality of corona wires removably mounted to a rigid support frame.